"1 cup" isn't a fixed volume worldwide. Two different standards are in common use, and mixing them up is one of the quieter reasons a recipe doesn't turn out the way you expected.
The US customary cup holds 236.59 mL (often rounded to 240 mL). It's the standard used by the vast majority of English-language recipes published online, and it's the one GramToCup uses everywhere — the calculator, every ingredient page, and both conversion charts.
The metric cup holds exactly 250 mL, about 5.7% more than the US cup. It's common in Australia, New Zealand, and some UK recipes — if a recipe's ingredient list uses grams alongside cups and reads like it was written outside the US, there's a reasonable chance it means this one.
5.7% sounds negligible for a single cup, but it compounds across a full recipe. As an illustration: 4 US cups of all-purpose flour weighs about 500g. If you filled that same "4 cups" using metric-cup-sized scoops instead, you'd end up with roughly 28g more flour than the recipe intended — enough to noticeably change a bread dough's texture or a cake's rise.
The more cup measurements a recipe stacks together, the more a mismatched standard shows up in the result.
Always the US customary cup (236.59 mL). Every density figure, every chart value, and every calculator result on this site is built on that convention — see the Cups to Grams guide for how those figures are calculated.
When you can, check where a recipe was published — the site, cookbook, or author's country is usually a reliable hint. When you can't tell, or when precision genuinely matters (bread, pastry, candy), converting to grams and weighing removes the ambiguity entirely, since a gram is the same everywhere regardless of which cup a recipe assumes.
Every conversion on GramToCup already uses the US customary cup — no guessing required.
Use the Gram to Cup Calculator →The US customary cup (236.59 mL), used throughout the calculator, every ingredient page, and every chart on this site.
A metric cup (250 mL) holds about 5.7% more than a US cup. That is small for a single cup, but it compounds in recipes that call for several cups of an ingredient.
Recipes rarely state it outright. As a rule of thumb, US-published recipes use the US cup; recipes from Australia, New Zealand, or some UK sources are more likely to use the metric cup. When in doubt, weighing in grams removes the ambiguity entirely.